This invention relates generally to process instruments used in industrial process control systems. More particularly, the present invention relates to a process transmitter having a modular, manually operated power generator.
Process transmitters are used to monitor process variables, such as pressure, temperature, flow and level, of process fluids used in industrial processes. For example, process transmitters are widely used in the chemical manufacturing and oil refining industries. Process transmitters are typically employed throughout industrial facilities at multiple locations to monitor a variety of process variables. Additionally, process transmitters are used in isolated field locations such as in cross-country pipelines.
Process transmitters include sensors that produce an electrical output in response to physical changes in the process variable. For example, capacitive pressure transducers or piezoresistive pressure transducers produce an electrical output as a function of the pressure of a process fluid. The electrical output of the sensor is processed by the transmitter circuitry so it can be monitored as an indication of pressure of the process fluid. Process transmitters also include electronics for either remotely or locally monitoring the electrical output. Remotely monitored transmitters include electronics that transmit the electrical output over a control loop or network to a central monitoring location such as a control room. Locally monitored transmitters include displays, such as LCD screens, that show the electrical output at the site of the process transmitter. Process transmitters typically draw their power through the control loop or network, or through power delivered through wiring systems typically found in industrial settings. In other embodiments, process transmitters include components for both local and remote monitoring.
However, in process transmitters that are located at extremely remote locations, such as on cross-country pipelines or oil and gas wells, it may be impracticable to directly deliver power to the process transmitter through either a control loop or wiring system. Nonetheless, it is necessary to have intermittent process transmitters situated along the pipeline in order to permit direct monitoring of the process fluid at the remote location.
Batteries and solar power have been the traditional method of delivering power to remotely located process transmitters. Conventional process transmitters include a terminal block for receiving the wiring associated with the control loop or power wiring systems. The terminal block is located within the housing of the process transmitter and includes terminals for receiving and securing the wires used to deliver the power. Typically the terminals are accessible from the exterior of the process transmitter housing through a conduit opening. The terminal block is connectable with power connectors inside the process transmitter housing that distribute power to the process transmitter electronics and sensor. Terminal blocks are modular and are easily removed from the process transmitter and replaced. A battery or a solar panel can also be coupled to the terminal block. Batteries eventually become fully discharged and therefore can be unreliable in field environments where replacement batteries are not readily available. Also, bringing replacement batteries into the field is burdensome even when they are available. Solar power can also be an unreliable source of energy due to unfavorable weather conditions that does not produce enough light to operate the transmitter.